1. Field of the Invention
The present invention relates to a magnetic field generating member used in a copier, facsimile, printer or the like as well as a magnetic particle support body, an image development device, a process cartridge and an image forming apparatus. For example, the present invention relates to a magnetic particle support body that forms a toner image by image developing an electrostatic latent image on an electrostatic latent image support body using a developer agent constituted from toners and magnetic particles. The present invention also relates to a magnetic field generating member used in such a magnetic particle support body and an image development device that includes such a magnetic particle support body. In addition, the present invention relates to a process cartridge and an image forming apparatus having such an image development device.
2. Description of the Related Art
A variety of image development devices that form an image using a so called binary developer agent including toners and magnetic carriers (described as developer agent hereinbelow) are used in an image forming apparatus of a copier, a facsimile and a printer or the like. This kind of image development device delivers the developer agent to an image development area facing a photosensitive drum (that is, the electrostatic latent image support body) and includes an image development roller (that is, the magnetic particle support body) that forms a toner image by image developing the electrostatic latent image formed on the photosensitive drum using the delivered developer agent.
The image development roller includes a cylindrical shaped image development sleeve constituted from non-magnetic materials and a magnet roller (that is, the magnetic field generating member) held inside the image development sleeve that generates magnetic force so that the developer agent is spike erected on the surface of the image development sleeve. In the image development roller, magnetic carriers contained in the developer agent spike erect on the image development sleeve along the magnetic lines (magnetic force) generated by the magnet roller and toners become attached to the spike erected magnetic carriers, that is, the developer agent is spike erected.
In recent years, electronic copiers and printers are increasingly colorized. These color image forming apparatuses require an image development device generally corresponding to 4 colors (yellow, magenta, cyan and black). In order for these image forming apparatuses to become smaller sized, the image development device also needs to be down-sized, which naturally leads to the down-sizing of the image development roller used in the image development device.
A smaller sized image development roller is realized by a magnet roller of a smaller diameter. However, when the diameter of the magnet roller becomes smaller, the volume of the magnet is reduced and magnetic force generated by the magnet roller is impaired. Therefore, when image development is performed using an image development roller with the magnet roller of a smaller diameter, deteriorations in quality of development images become problematic. Propositions to solve this problem are made in JP 2000-243620A.
The main body part of a magnet roller proposed in JP 2000-243620A includes a cylindrical column-like shaped ferrite resin magnetic body and a rare-earth resin magnetized body fixed in a concave groove disposed along an axial direction of the cylindrical column-like body in the external circumference surface of the cylindrical column-like body. The main body part of this magnet roller is shaped by magnetic materials and includes the rare-earth resin magnetized body having high magnetic force so that a magnet roller of small diameter but high magnetic force can be obtained.
However, the main body part (including the axial part) of the magnet roller proposed in JP 2000-243620A is shaped by a ferrite resin magnetic body of an inferior strength. Furthermore, the concave groove is disposed in the external circumference surface of the main body part. Therefore, stiffness of the magnet roller becomes insufficient and the magnet roller is subject to easy flexure. Thereby deformation due to time lapse or warpage and deflection of the magnet roller or the like is inevitably generated at times. Therefore, magnetic force on the surface of the image development roller becomes non-uniform during image development operations so that irregularities are generated to the spike erections of the developer agent and quality of development images deteriorates problematically.
In addition, because of the flexure of the magnet roller due to insufficient stiffness, there is a possibility that the rare-earth resin magnetized body fixed to the magnet roller might be bent and damaged so that during usage of the magnet roller, malfunction of the image development device or the like is triggered and during storage of the magnet roller, defective products are yielded despite their not even being in-use. Therefore, reliability and product quality deteriorates problematically.